How your Heart beats…In this Power-point:• The structure of the Heart• How a valve works• The Cardiac Cycle• Control of the beat• Parts of the blood

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http://www.heart-valve-surgery.com/Images/heart-cartoon.jpg

External view of the heart

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The internal structure of the heart

Simple diagram of the heart

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How a valve works……

The heart valves work in much the same way. (esp. the semi lunar valves)

The bi-cuspid and tri-cuspid valves have tendons to stop them being pushed inside-out.

http://wiki.nus.edu.sg/download/attachments/22053011/one_way_vein_valves.jpg.jpg

Right Atrium

Right Ventricle

Left Atrium

Left Ventricle

Watch the whole thing first before splitting it into sections…….

Notice how both atria fill at the same time, then both ventricles fill then empty at the same time

Next look at the valves. Try to follow how the valves co-ordinate with the beating of the atria and ventricles

Now look at the flow of the blood. The blood comes into the atria from the Vena cava and pulmonary vein, goes into the ventricles and is then pumped past the semilunar

valves into the aorta or pulmonary artery

The heart beats on average 70 times every minute and is continuous. The beat is Myogenic – It beats without external impetus. (Remember the scene from Indiana jones and the temple of doom

where the priest removes the heart and it continues to beat………..)

.

http://img2.timeinc.net/ew/dynamic/imgs/080715/Death-scenes/Indiana-Jones-heart_l.jpg

• The periods of contraction are called systole. There are 2 periods of systole – atrial followed by ventricular.

• The periods of relaxation are called diastole. The whole heart – atria and ventricles go into diastole at the same time.

• Atrial Systole →Ventricle systole→ Diastole→ Atrial Systole →Ventricle systole→ Diastole……….

Atrial Systole

• The Atria contracts• The blood is pushed

against the AV valve which opens.

• Vena Cava and pulmonary vein valves are shut.

• The blood flows into the ventricle.

http://upload.wikimedia.org/wikipedia/commons/thumb/3/34/Heart_systole.svg/200px-Heart_systole.svg.png

Ventricular Systole

• The ventricle contracts.

• This pushes blood against the AV valve and closes it.

• The semi lunar valves open,

• Blood flows into the Aorta or Pulmonary artery.

http://upload.wikimedia.org/wikipedia/commons/thumb/3/34/Heart_systole.svg/200px-Heart_systole.svg.png

Diastole

• All the muscles relax.• The semi-lunar valves

close.• Pulmonary vein and

vena cava valves open.

• Blood flows into the atria AND ventricles.

http://upload.wikimedia.org/wikipedia/commons/thumb/3/34/Heart_systole.svg/200px-Heart_diastole.svg.png

Or in more depth………• The cardiac cycle• One cardiac cycle consists of the atria and then the ventricles contracting so

that the blood that has entered the heart is pumped out. This occurs about• We shall start when the atria and ventricles are in diastole.• Blood at a low pressure in the veins flows into the atria. This increases the

pressure inside the empty atria as they fill. Some of the blood trickles through the open atrioventricular valves into the relaxed ventricles below.

• When the atria are full, they go into atrial systole, their walls contract and blood is pushed through the valves into the ventricles. The pressure in the atria is increased due to the contractions and the pressure is increasing in the ventricles as they fill with blood.

• When the atria contract, blood cannot flow back into the veins because the pressure of the blood pushes on the valves in the veins to shut them.

• After a short delay the ventricles contract from the apex (base) upwards. The pressure inside the ventricles increases due to the ventricular systole. As the pressure increases to a higher level than the pressure in the atria, blood pushes against the atrioventricular valves, shutting them (the first heart sound) and preventing backflow.

• The semilunar valves open under the pressure and blood leaves the heart.• The ventricles relax - ventricular diastole - and the semilunar valves snap

shut behind the blood (the second heart sound).

So how does the pattern of beat work?

Click on the link below. Turn off the sound and watch. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html

You need to know about:The flow of impulse from the Sino-Atrial Node or Pacemaker across the atria.The inability of the impulse to pass directly to the ventricles………..but the Pick up of the impulse at the Atrio-ventricular node.The passing of the impulse down the Purkinje fibers to the bottom of the heart……Causing the contraction of the ventricle upwards

Within the right atrium there are a specialise group of cells called the Sino Atrial Node.(SAN).

These cells can generate an electrochemical potential across the cell membrane and once threshold is reached this can be propagated across the other cells of both atria.

The speed of conduction across the two atria is fast enough that both effectively contract together.

However the cell membrane structure alters across a line rough consistent with the diagram and effectively prevents the conduction of the contraction stimuli traveling down into the ventricles

In Summary

http://click4biology.info/c4b/6/hum6.2.htm

A) The impulse is picked up by a specialised group of cells in the right atrium wall called the Atrio-Ventricular Node (AVN).B) The AVN conducts the impulse down through the central septum of the heart along specialised fibres called the Purkinje fibers. The fibres are insulated from the muscle and do not cause contraction. C) The impulse emerges into the muscle at the apex of the heart so that the ventricular contraction begins at the apex.D) The impulse travels on emerging into the heart muscle higher up the ventricle wall in this way the contraction spreads upwards.

Note that this direction of contraction pushes the blood towards the semi-lunar valve and also not that the transmission time down the Purkinje tissue creates a delay between atrial and ventricular systole. This delay maintains the correct directional flow of blood through the different chambers.

http://click4biology.info/c4b/6/hum6.2.htm

What controls how fast or slow the heart beats?

• Accelerator Nerve into the Sino-Atrial Node speeds up the pulse from resting beat, The Decelerator Nerve (Vagus) slows down the pulse rate. These nerves are controlled by the cardiac center in the Medulla Oblongata of the brain.

http://scienceaid.co.uk/biology/humans/images/heartnerves.jpg

• Adrenalin released from the adrenal glands also acts on the Sino-atrial Node to speed up the pulse from resting beat, this is a Fight or Flight response.

The adrenalin is carried to the heart in the blood stream.

http://www.coolschool.ca/lor/BI12/unit13/U13L02/adrenalglands.png

The blood is made up of 3 main types of cell

1. Red blood cells (erythrocytes)

- are responsible for the carriage of oxygen.

- have no nucleus so they can carry more haemoglobin.

- are small and able to pass through small capillaries.

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White blood cells (leukocytes)……

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2. Phagocytes – gobble up large invaders such as bacterial cells and amoeba by process of phagocytosis (“cell eating”- like a pac-man!) They have a multi-lobed nucleus so that they can pass out of the blood vessels to fight infection. These form the majority of Pus!

3. Lymphocytes – produce antibodies to fight off the smaller invaders such as viruses. The large nucleus is highly active in producing the antibodies. These cells stay in the blood vessels and lymph vessels.

Blood plasma

The rest of the blood is Plasma and platelets. This is responsible for the other functions of the blood:

• Carriage of dissolved products of digestion

• Carriage of dissolved waste products of metabolism

• Carriage of dissolved hormones – chemical messengers

• Carriage of heat• Carriage of Carbon Dioxide

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Structure of Blood vessels

Why is it important to have elastic fibers in the arteries?

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Structure of Arteries

• Thick walls

• No valves

• Elastic tissue

• Keep blood at high pressure

• Always Away from the heart

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Structure of Veins

• Veins have valves and thin walls because the blood pressure is low and they need to stop “backflow”!

• They have much less elastic fiber to resist the pressure.

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Structure of Capilliaries• Very thin walls to allow

easy diffusion.• Narrow to allow cells

through in single file• Very many capillaries to

deliver blood to all the tissue.

• Are leaky – to allow the tissue fluid with all its disolved nutrients to bath the body cells.

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